A team of scientists has discovered a hidden torrent of rubbish flowing through London after collecting thousands of pieces of plastic submerged along the river bed of the upper Thames Estuary.

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The sheer amount of plastic recovered shows there is an unseen stream of trash flowing through the capital which could be a serious threat to aquatic wildlife.

The findings, published online in Marine Pollution Bulletin, highlight the cause for concern, not only for ecosystems around the river but for the North Sea, in to which the Thames flows.

Using nets designed to catch Chinese mitten crabs, scientists from the Royal Holloway, University of London, and the Natural History Museum documented rubbish collected during a three-month trial.

More than 8,000 pieces of plastic were collected, including large numbers of cigarette packaging, food wrappers and cups, but more than a fifth of waste was made up of sanitary products.

Dr Dave Morritt, a Senior Lecturer in Marine Biology at Royal Holloway and co-author of the study says: "The unusual aspect of the study is that these nets are originally designed to trap fish and crabs moving along the river bed, so we can see that the majority of this litter is hidden below the surface."

“This underwater litter must be taken into account when predicting the amount of pollution entering our rivers and seas, not just those items that we can see at the surface and washed up on shore. The potential impacts this could have for wildlife are far reaching: not only are the species that live in and around the river affected, but also those in seas that rivers feed into."

The waste collected for the study is only a small snapshot of the volume of litter which may exist at the bottom of the Thames. Plastic bags and other large items were unlikely to get caught in the small nets so the true extent of the problem is still unknown.

Dr Paul Clark, a researcher, at the Natural History Museum and co-author of the study says: "All of this waste, which was mostly plastic, was hidden underwater so Londoners probably don't realize that it's there."

"Plastic can have a damaging impact on underwater life. Large pieces can trap animals but smaller pieces can be inadvertently eaten."